June 4, 2010 -- Preliminary research calls into question the old adage that stretching improves flexibility more than resistance training.

"Our results suggest that full-range resistance training regimens can improve flexibility as well as, or perhaps better than, typical static stretching regimens," says James R. Whitehead, EdD, of the University of North Dakota in Grand Forks.

Also known as strength training, resistance training usually involves in order to build muscle. You can also increase your strength by pushing or working against something that resists your weight, such as doing push-ups.

"There's an old notion that if you do resistance training, you have to stretch those muscles too," Whitehead tells WebMD. "It's a hangover to the myth that muscles lose flexibility as they get bigger."

Resistance Training Improves Flexibility, Strength

An extensive search of scientific literature review failed to turn up any studies where strength training was actually pitted against stretching to see which better improves range of motion, Whitehead says.

So the researchers compared the two techniques' effect on flexibility of different muscles and joints in 25 college-age volunteers.

Participants were randomly assigned to strength training or stretching programs focusing on the hamstring muscles and hip, shoulder, and knee muscles and joints for five weeks. As a comparison group, 12 other students engaged in neither type of exercise.

Tests of flexibility and strength at the end of the five weeks showed:

Both stretching and strength training performed equally well at improving hamstring flexibility, and both were superior to no exercise.

Resistance training was superior to no intervention at improving hip flexibility, but stretch training was no better than doing nothing.

There were no differences between the groups when it came to shoulder extension flexibility.

Resistance training was superior to no intervention at building knee strength.

The findings were presented at the American College of Sports Medicine's annual meeting in Baltimore.

Findings on Resistance Training 'Not Surprising'

"Resistance training produced greater improvements in flexibility in some cases, while also improving strength," Whitehead says.

The preliminary study was small and the findings need to be replicated in larger numbers of people, he says.

"But if they hold up with replication, people really don't have to be worried about doing stretch exercises whenever they're doing resistance exercises," Whitehead says.

William Lunn, PhD, an exercise scientist at the University of Connecticut, tells WebMD he's not surprised by the results.

"If you do resistance training -- especially if you focus on full range of motion -- you would promote flexibility," he says.

This study was presented at a medical conference. The findings should be considered preliminary as they have not yet undergone the "peer review" process, in which outside experts scrutinize the data prior to publication in a medical journal.

SOURCES: American College of Sports Medicine's 57th Annual Meeting, Baltimore, June 1-5, 2010.

James R. Whitehead, EdD, University of North Dakota, Grand Forks.

William Lunn, PhD, associate professor of exercise science, University of Connecticut.